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Plaster defects can be easily avoided in the construction stage if the necessary precautions are taken at the right time. The preventive measures range from proper preparation and cleaning of the wall surface to selecting suitable materials and following the standard construction procedures.

A clean and adequately prepared wall surface ensures good bonding on a plaster-wall interface, preventing the delamination of the plasterwork. The exposure of the plaster to wind and sunlight should be prevented to avoid plastic cracks. Additionally, a proper curing regime for a minimum of ten days guarantees the achievement of adequate strength and prevention of shrinkage crack development.

Different types of defects observed in plastering work are blistering, cracks, efflorescence, flaking, peeling, popping, softness, and uneven surfaces. These problems affect the aesthetic appearance of the building.

How to Prevent Plaster Defects in Construction Phase?

1. The use of well-graded sand can prevent the development of crazing cracks. Crazing cracks are the network of cracks that have hexagonal patterns. The crazing cracks are shallow and do not extend to the full depth of the plaster.

2. Remove wall surface from loose material and clean it from dust and oil to avoid plaster debonding.

3. The use of cement slurry or spatterdash coat before plastering can improve bonding and reduce debonding or delamination.

4. Avoid the use of pure cement for the finishing coat.

5. Avoid using the mortar mix rich with cement; use a mix ratio of one part of cement to four parts of sand depending on the type of sand.

6. Consider the use of fly ash blended cement because it releases low hydration heat and has a low possibility of crack development as compared to ordinary Portland cement.

7. Wet the masonry wall with a sufficient amount of water before beginning the plastering work to prevent water absorption in the mortar mix by brick wall.

8. The absorption of water by the brick wall would increase the loss of moisture in the mortar mix and increase the possibility of plastic shrinkage crack development.

9. Do not overwork the cement finishes.

10. Begin curing as soon as possible, especially in hot and windy conditions.

11. Cure the plaster adequately for at least ten days.

12. Prevent grinning through the provision of an undercoat plastering and two coats of plaster on a firm surface. Grinning is the appearance of masonry joints through plasterwork.

13. Protect plasterwork from sunlight and wind to avoid rapid drying to hinder the development of plastic shrinkage cracks.

14. Commence the plastering work at a suitable time to prevent sun and wind exposure.

15. Use a sand with fineness modulus ranging from 2.4 to 2.6.

16. Use plaster thickness of 1.5 cm or less.

17. Plaster with a thickness of more than 2 cm is likely to suffer from drying shrinkage cracks. Excessively thick plaster leads to debonding and delamination.

18. After hardening, the loss of moisture makes the plaster to shrink and, consequently, develops cracks (drying shrinkage cracks).

19. If a higher plaster thickness is needed, apply two plaster layers with a gap of around three days. Use a thickness of about 1.2 cm thickness for each layer.

20. Sand with a fineness modulus less than 2.2 results in drying shrinkage cracks.

21. The plaster surface may suffer from popping if it contains substances such as seeds and dead burnt lime.

22. Remove the efflorescence by brush washing the plaster surface with a mix of one part of hydrochloric acid or sulphuric acid and five parts of water. After washing, dry the affected area.

23. Efflorescence is a whitish crystalline substance on the plaster surface. It appears due to the presence of salt in construction materials like bricks, water, sand, etc. So, consider the possibility of efflorescence occurrence during the selection of construction materials.

24. The surface of a plaster may show rust stains if it is applied on a metal background.

Plastic Shrinkage Cracks
Figure-1: Plastic Shrinkage Cracks
Drying Shrinkage Cracks
Figure-2: Drying Shrinkage Cracks

FAQs

What is plastering in civil engineering?

Plastering is the process of covering walls or uneven surfaces of buildings with plaster. Plaster is a thin layer of mortar applied over the masonry surface that acts as a damp-proof coat over the brick masonry work.
It also provides a finished surface over the masonry that is firm and smooth; hence, it enhances the building’s appearance. Read more about it here.

What are the common defects observed in plaster?

Different types of defects observed in plastering work are blistering, cracks, efflorescence, flaking, peeling, popping, softness, and uneven surfaces. These problems affect the aesthetic appearance of the building. Read more about it here.

How to prevent plastering defects?

The preventive measures range from proper preparation and cleaning of the wall surface to selecting suitable materials and following the standard construction procedures. A clean and suitably prepared wall surface ensures good bonding on a plaster-wall interface, preventing the delamination of the plasterwork.
The exposure of the plaster to wind and sunlight should be prevented to avoid plastic cracks. Additionally, a proper curing regime for a minimum of ten days guarantees adequate strength achievement and hinders shrinkage crack development.

Why does plaster crack as it dries?

Drying shrinkage cracks occur due to the rapid loss of moisture after the hardening of plaster. Excessive shrinkage creates tensile stresses greater than the tensile strength of the plaster. Thick plaster tends to suffer from drying shrinkage cracks.

Read More

Special Plastering Materials for Different Purposes Used in Building Construction

Plastering Concrete Surfaces – Methods and Procedure

Work Procedure of Plastering on Masonry Surfaces

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Madeh Izat Hamakareem

Madeh Izat Hamakareem

EDITOR
Madeh is a Structural Engineer who works as Assistant Lecturer in Koya University. He is the author, editor and partner at theconstructor.org.

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